Papermachine headbox discharge velocity indicator



Aug. 22, ER

PAPERMACHINE HEADBOX DISCHARGE VELOCITY INDICATOR Filed Dec. 16, 1964 i 2 Sheets-Sheet 1 N Q Q N 1 Q 1|; I N W i I, e W & LL h I N VENTOR.

dose 06 0 /%'n 9/ My wVW ATTORNEYS Aug. 22, 1967 j PARKER 3,337,393

PAPERMACHINE HEADBOX DISCHARGE VELOCITY INDICATOR Filed Dec. 16, 1964 2 Sheets-Sheet 2 g A 572 Ila]! 4/ z Z9 INVENTOR.

c/ase n/v 0 Parker ATTORNEYS United States, Patent 3,337,393 PAPERMACHINE HEADBOX DISCHARGE VELOCITY INDICATOR Joseph D. Parker, Beloit, Wis., assignor to Beloit Corporation, Beloit, Wis., a corporation of Wisconsin Filed Dec. 16, 1964, Ser. No. 418,799 9 Claims. (Cl. 162-263) ABSTRACT OF THE DISCLOSURE This invention relates generally to papermaking apparatus. More particularly, the invention relates to means for determining the discharge velocity head of stock flowing from the slice opening of a headbox, which is constructed so as to subject the stock flowing therethrough to a substantial pressure drop due to friction losses up stream of the slice opening thereof, onto paper forming apparatus such as a forming wire, whereby the velocity of the stock flowing from the slice opening can be maintained at a velocity proportional to the speed of the forming wire.

In conventional rectifier roll-type headboxes, which may be of the air pressure-loaded type, the velocity of the stock flowing in the headbox is normally so low and the frictional drag losses from the rectifier rolls and slice approach channel so small that a sufiiciently accurate indication of the discharge velocity head of the stock as it flows from the slice opening is the static pressure head existing close to the floor of the headbox upstream of the slice rectifier rolls. This static pressure head is indicated simply and directly by means of a standpipe, manometer or similar apparatus capable of producing an output sig nal in response to a pressure signal from a pressure tap in the headbox.

A single static pressure head measurement as this cannot be used for a direct discharge velocity head indica tion in headboxes in which friction losses subsequent to the point of measurement are appreciable compared to the discharge velocity head at the slice opening. The as son for this is that the single static pressure head measurement would have to be corrected for the subsequent frictional head loss, and this correction would vary with variation in the stock flow rate. As will be understood by the artisans, it is not feasible to place a Pitot tube or the like device within the headbox in the stream of stock upstream of the slice opening for many reasons, not the least of which is the deleterious effect such device would have upon the uniformity of the stock flowing to the forming wire across the width of the wire.

By means of the present invention, however, the discharge velocity head of the stock as it flows from the slice opening can be simply and conveniently indicated even in headboxes constructed such as to produce relatively high friction losses immediately upstream of the slice opening, and without the necessity of placing obstructions within the stock stream.

Briefly, the invention comprises an analog computer device which senses the static pressure of the stock at two points in the stock supply and headbox system. This de* 3,337,393 Patented Aug. 22, 1967 ice vice is of such dimensions that the slice discharge velocity head is indicated directly by a single indicator, that is by a single manometer leg level. This design can be used over a wide range of headbox designs, stock pressures and velocities and pressure drops due to friction losses upstream of the slice opening.

It is, therefore, an object of the invention to provide means for indicating the discharge velocity head of stock flowing from the slice opening on the headbox, even wherein the.headbox is constructed so as to produce a substantial pressure drop due to friction losses immediately upstream of the slice opening.

Another object is to provide, for a headbox of the type described, means for indicating stock discharge velocity head, obviating measuring devices within the stock stream and the disadvantages attendant thereto.

Still another object of the invention is to provide a method and apparatus for determining stock discharge velocity head as a function of the static pressure of the stock at two points in the stock supply system.

Still a further object of the present invention is to provide a method for determining the configuration and calibration of a manometer constructed in accordance with the principles of the invention.

Many other features, advantages and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description which follows and the accompanying sheets of drawings, in which preferred structural embodiments incorporating the principles of the present invention are shown by way of illustrative example only.

On the drawings:

FIGURE 1 is asomewhat schematic drawing of the headbox end of a papermaking machine including means for determining the discharge velocity head of stock flowing from the slice opening thereof, constructed in accordance with the principles of the present invention;

FIGURE 2 is a schematic drawing of an exemplary manometer useful in explaining the principles of the invention;

FIGURE 3 is a vertical elevational view of an exemplary manometer useful in applying the principles of the invention;

FIGURE 3A is a top plan view of the middle leg of the manometer shown in FIGURE 3; and

FIGURE 4 is an enlarged view of an indicating leg of the manometer illustrated in FIGURE 3.

As shown on the drawings:

As previously noted, in many headboxes the velocity of stock flow within the box is normally so low and the frictional drag losses, as a result of rectifier rolls and the slice approach channel, so small that a sufliciently accurate indication of the discharge velocity head of the stock flowing from the slice opening is the static pressure head existing close to the floor of the headbox upstream of the slice rectifier rolls.

However, in headboxes in which the friction losses upstream of the slice opening and downstream of the point of measurement are appreciable compared to the discharge velocity head a single static pressure head measurement cannot be used for a direct discharge velocity head indication.

For example, :an exemplary headbox is indicated at reference character 10 and comprises a long, narrow slice approach channel 11 for delivering stock from the interior 12 of the headbox 10 to a slice opening indicated at 13, the dimensional characteristics of which are determined by a vertically reciprocally movable slice 14.

The stock which flows from the slice opening 13 is directed to a traveling paper forming surface such as a forming wire and as will be understood by those skilled in the art it is helpful for the papermaker to know the discharge velocity of the stock as it leaves the slice opening so that it can be regulated in proportion to the velocity of the forming wire.

A stock supply system indicated generally at 16 is utilized to convey stock from a pressurized source to the headbox and more particularly comprises a stock supply header 17 and a stock supply manifold 18 interconnecting the headbox 10 and the supply header 17.

The exemplary headbox illustrated in FIGURE 1 is of the pressurized type and comprises a closed top end 19 for developing a pressurized air cushion therebelow at 20 above a level 21 of stock within the headbox 10.

If the slice approach channel 11 were very short and the pressure drop of the stock flowing therethrough was negligible, the discharge velocity head of the stock flowing from the slice opening 13 could be easily determined.

For example, there are many zones within the headbox 10 wherein the velocity of the stock flowing therethrough is negligible. Assume that such zero velocity condition exists at point A along a back wall 22 of the headbox and that a pressure tap is provided at point A in order to determine the static pressure. It will be appreciated that the total head of the stock at point A, which is at the same elevation as the slice opening 13, is equal to the static pressure head, since the velocity head is negligible.

It will further be appreciated that A= v-lrA (1) Although in the illustrated embodiment point A is at the same elevational level as the slice opening, it could just as well be above or below the slice opening with suitable correction for the increased or decreased static pressure head as a result of a different elevation.

Referring to Equation 1 it will be appreciated that in instances where the pressure drop between the interior of the headbox and the slice opening is negligible, the term H approaches zero and H is equal to H In the exemplary headbox illustrated in FIGURE 1, however, wherein the pressure drop through the long, narrow channel 11 is substantial, the static pressure head measurement at point A (H would have to be corrected for the frictional head loss through the channel 11, and this correction would vary with the stock flow rate.

A single static pressure head measurement that needed correction such as this would not be a convenient, practical tool for the papermaker. It is highly desirable to have a device which will provide a direct indication of the discharge velocity head of the stock from the slice opening 13 which is substantially independent of the stock flow rate and of the slice opening.

In accordance with the principles of the present invention the discharge velocity head can be accurately determined over a wide range of flow rates and a wide variety of headbox constructions through ascertainment through the utilization of a device such as a manometer of the difference in static pressure head between the quiescent zone A in the headbox 10, wherein the static pressure head is substantially equal to the total head, and at a point in the stock supply system wherein the static pressure head is substantially less than the total head.

In order to determine the static pressure head at a point B in the stock supply header 17, a riser or standpipe 23 in fluid communication with the interior of the header 17 is extended vertically upwardly from the wall of the header. Another standpipe 24 is connected to the headbox 10 at point A and is in fluid communication with the interior 12 thereof. The top end-s of the standpipes 23 and 24 are connected in fluid communication with the air cushion in the top end 20 of the headbox 10 in order to balance the pressures acting on the levels of the stock therein, and to obviate unnecessary height of the standpipes in order to compensate for the pressurization of the headbox 10.

Referring to FIGURE 2, an exemplary device for measuring the difference in static pressure heads between point A and a point B, which is located in the standpipe 23 at the same elevational level as point A for the sake of sim plicity of evaluation, is illustrated as comprising a manom eter indicated generally and schematically at reference numeral 26 having a pair of legs 27 and 28 extending upwardly in a vertical direction and interconnected by means of a tube 30, from which a third leg 29 rises in fluid communication with legs 27 and 28.

Assume that a top end 31 of the leg 27 is connected by means of a conduit 32 to pressure tap A of the headbox 10, and a top end 33 of manometer leg 28 is connected by means of a conduit 34 to pressure tap B. It is again noted that point A can be located at any zone of quiescence in the stock supply system, and normally available at many places within the headbox, and points B and B, can be located, correspondingly, at any point in the stock supply system wherein the static pressure head is substantially less than the total head.

Assume that the frictional head loss between pressure taps B and A is H so that the static pressure head sensed at pressure tap B consists of four component parts in accordance with the following equation:

tions:

H =K Q (3) fB fBQ where Q is equal to the total flow rate through the headbox 10 and K K M and N are factors determined by the geometry of the flow system. In most commercial headbox systems of fixed geometry, operating at fairly high Reynolds numbers, these factors are substantially constant over a wide range of flow rates.

Assume, as noted, that pressure tap B is located at a point Where the flow velocity is not very high so that the kinetic head (H is not exceptionally large compared to the other terms in Equation 2. Then, since the mag-nitude of N is generally just slightly less than 2.0 and H varies with the flow rate to the 2.0 power, a reasonable simplification is to combine the H and H terms such that Then combining Equations 1, 3 and 6, we obtain an expression for the discharge velocity head:

M Hv HA KA KB N 7 It is now desirable to adjust the dimensions of the manometer 26 so that the discharge velocity head H is indicated directly by the displacement of a single liquid level of the fluid F therein in one of the legs thereof.

For purposes of illustration, we will assume momentarily that M =N and that K divided by K =K, a constant.

Equation 7 then becomes:

At zero stock flow through the headbox 10, the liquid level in each of the three legs 27, 28 and 29 of the manometer 26 are the same at level 00. After a steady stock flow has been established, the levels are displaced vertical distances Y Y and Y as shown in FIGURE 2. Thus a a H,-(K +K+1 Y S+(l K )Y S (12) Assume that the areas A and A are adjusted so that and . Then the last term of Equation 12 drops out and H,,

becomes a function of Y only, according to the following equation:

Thus, the discharge velocity head is indicated directly and uniquely by the liquid level displacement in leg 27. That is, under the general conditions assumed and with K being a positive number, it is possible to have this direct indication by a single level displacement in leg 27 only.

We now consider the more general case where the values of M and N are not the same. If we combine Equations 9, 10 and 11 with Equation 7 we obtain an expression for H analogous to Equation 12:

This function f can be expanded to first order terms by the Taylor method about two arbitrarily selected values of Y and Y i.e., Y =a and Y =b. Therefore the function of Equation 16 is approximated by the expression Since it is intended to use this approximation over the range of values of Y and Y encountered for any particular installation or headbox design, the values of small a and b intuitively would be selected from the middle of the range anticipated. Partially differentiating Equation 16, substituting into 17 and then substituting the result into Equation 15, we then have a linearized expression for H M s M M 4, l N (K; m n 112] where Hence H becomes a function only of Y under the condition that When M=N, Equation 20 reduces to Equation 13, and

as before.

Under conditions imposed by Equation 20 then, the

discharge velocity head is approximately indicated by the displacement Y according to:

For fixed geometry systems, the last term in Equation 22 is constant and it should be noted that Equation 22 is identical with Equation 14 except for the addition of this constant term. It will be explained hereinafter how this relationship can be used for calibrating the manometer utilized in the system.

It is next desirable to discuss the practical considerations which determine the manometer dimensions.

From Equation 21 and 22 it can be seen that the vertical displacement Y for a given discharge velocity head in a particular headbox can be increased by (a) decreasing the specific gravity S of the manometer fluid F, (b) decreasing the area ratio A /A and (c) increasing K by moving the pressure tap B further upstream. However, once pressure tap B has been located, the only practically effective way to increase Y is to decrease the specific gravity S of the manometer fluid F, since the effect of decreasing A /A becomes small when this area ratio becomes much smaller than 1.0. But decreasing S is accomplished at the cost of making Y and hence the length of leg 29 greater. A suitable choice for the specific gravity S of the manometer fluid F, then, must be compromised between a value low enough to provide an adequately large Y displacement and one great enough to keep the length of leg 29 reasonable.

To illustrate the development of a practical manometer design, assume a headbox installation where k =560 ft./(Ft. /sec./in. width) K ft./(Ft. /sec./in. width) the displacement Y Assume that A /A is arbitrarily chosen as equal to 0.05. To determine a suitable value for S, we note that the order of magnitude of SG is close enough to unity so that can be reasonably assumed as being equal to 1.0. Thus, according to Equation 20,

8.56 Substituting Au 3O.05 and 3-8.56

into Equation 22, and assuming SG is=to 1.0, we have for H =9.7l, the maximum displacement Y Furthermore from Equations 6, and 11, we can deduce that 60 g.p.m./in. of width, respectively), we have for the maximum Y From Equations 23 and 25, it is evident that both Y and Y increase as S decreases, but Y increases approximately 20 times faster. A suitable manometer fluid F in this example has a specific gravity of 2.95. With such fluid, the maximum Y displacement would be about 7.3 feet and the maximum Y displacement about 4.35 inches.

Choosing S=2.95, we then calculate the exact value of A /A required for the manometer in order for Equation 22 to hold. Equation 20 indicates that A /A depends upon the values we choose for Y =a and Y =b, but it will become apparent that A /A is not very sensitive to changes in a or b. Therefore, we can determine roughly the range of displacements Y and Y and choose a and b values from within this range.

Assume then that the lower limits of Y and Y occur at a discharge velocity of 1,000 f.p.m. and a flow rate of 40 g.p.m. per inch of width. The corresponding minimum Y and Y values calculated are 2.0 inches and 3.3 ft., respectively. From near the middle of the ranges, then arbitrarily make a=0.25 ft. and b=5.0 ft. From Equation 20 then calculate Summarizing, the specifications for the manometer to fit this particular exemplary headbox are:

The discharge velocity head is indicated approximately by the liquid level displacement Y given by the relationship obtained from Equation 22:

H =28.3 Y O.53 (26) To illustrate the accuracy of this approximation, values of H calculated from Equation 26 are compared with those determined by the rigorous relationship of Equation 15 over a range of discharge velocities and flow rates as shown in the following Table I:

TABLE I Velocity Head, Hv, it. Flow rate, Q, Discharge g.p.m. in. Velocity. f.p.1n.

From Eq. 15 From Eq. 26

It is apparent from the comparison as shown in Table I that the accuracy of this approximate velocity head indication is within acceptable experimental units and is certainly adequate for papermakers use. In general, the more nearly alike that M and N are and the greater the discharge velocity head compared to the friction head loss, the better is this approximation.

Since Y in this example has a maximum value of only 4.35 inches, leg 27 should be inclined to magnify this displacement. Referring to FIGURES l and 3, the manometer indicated generally at reference character 26 in FIGURE 2 is indicated therein at reference character 26a. The manometer legs 27, 28 and 29 in FIGURE 2 correspond, respectively, to the legs 27,, 28 and 29,, of FIGURES 2 and 3.

As noted, leg 27,, should be inclined to magnify the displacement of Y and a suitable angle of inclination (6) is about 7.7", so that a vertical displacement of 4.35 inches equals about 32.5 inches along the inclined leg 27,,

The relationships are slightly changed by making leg 27 inclined, but are easily adjusted by replacing A with A1 sin 0 where, as noted above, 0: angle of inclination of leg 27,. Equations 19 and 22 then become G=b -a 51mm) No correction needs to be made to A /A and the new A /A value is simply 0.05 (sin 0):0.0066. Consequently, using a inch inside bore tube for the inclined leg 27,, leg 29,, must have a size equivalent to a round pipe with a 2.69 inch inside diameter and leg 28,, must be equivalent to a pipe having an inside diameter of 7.87 inches.

The manometer 26,, shown in FIGURES 1 and 3 is illustrative of a design based on the above relationships, although it will be apparent that the relative sizes and [lengths of legs 27,, 28,, and 29 are not directly proportional to the above relationships.

As shown in FIGURE 4, a scale 36 or similar indicia may be marked along the leg 27,, in order to represent discharge velocity head therealong. A flow restriction orifice 37 may be installed at the bottom leg 29,, to inhibit surging when the pressure in the headbox 10 is suddenly released at shut downs. A needle valve 38 and a drain valve 39 may also be incorporated in the manometer 26,, as illustrated in FIGURE 3. In addition, it is important that no air pockets are trapped in the fluid filled portions of the manometer 26,, since this performance depends on a constant volume of fluid.

As noted, an object of the invention is to provide means for determining the discharge velocity of the stock at the slice opening so that it can be correlated with respect to the speed of a paper forming surface such as a forming wire. Since the actual values of K K M and N are normally not known, the manometer 26,, can be adjusted and calibrated in position on the papermaking machine during actual operation. For this purpose, the cross-sectional area of leg 29,, can be made adjustable by constructing it with an oversized inside diameter and suspending, successively, a plurality of solid rods as at 40 having progressively larger diameters into the leg from the top open end 41 thereof. The correct value of the ratio A /A is determined by means of Equation 28 and some independent method of measuring the stock discharge velocity head at the slice opening.

Thus, for measurements of H at two different discharge velocities, Equation 28 states that the corresponding change in Y must be equal to:

AH A, A

AY Sll'l 6+ ;+1 S (29) when A /A has the correct value. Such correct value of A /A can be deduced by a process of trial and error by changing the area A by means of the solid rods and comparing the observed change in Y with the change in Y predicted by Equation 29.

After the manometer 26 has been calibrated, the discharge velocity of the stock can be correlated with the speed of the forming wire by vertically adjusting the slice 14 or by varying the flow rate of the stock.

Although minor modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such modifications as reasonably come within the scope of my contribution to the art.

I claim as my invention:

1. A papermaking machine comprising,

a stock headbox for receiving stock from a supply system,

a slice opening for delivering stock to a paper forming apparatus such as a forming wire,

a channel for convening the stock from said headbox to said slice opening and producing a reduction in the static pressure of the stock therethrough due to friction losses,

pressure measuring means for connection to the supply system and to said headbox for determining the pressure differential between a point in the supply system at which the static pressure head is substantially less than the total head and a point in said headbox below the level of stock therein and at a zone of quiescence.

2. A papermaking machine comprising,

a stock supply system for supplying pressurized stock to a headbox,

a stock headbox for receiving stock from said supply system,

a slice opening for delivering stock to a paper forming apparatus such as a forming wire,

a channel for conveying stock from said headbox to said slice opening and producing a reduction in the static pressure of the stock therethrough due to fricton losses,

pressure measuring means for connection to the supply system and to said headbox for determining the pressure differential between a point in said supply sysstem at which the static pressure head is substantially less than the total head and a point in said headbox below the level of stock therein and at a zone of quiescence, and

indicating means associated with said pressure measuring means for indicating the discharge velocity head of the stock at said slice opening as a function of said pressure differential.

3. A papermaking machine comprising,

a stock headbox for receiving pressurized stock from a supply system,

a slice opening for delivering stock to a paper forming apparatus such as a forming wire,

a channel for conveying stock from said headbox to said slice opening and producing a reduction in the static pressure of the stock therethrough due to friction losses,

pressure measuring means for connection to the supply system and to said headbox for determining the pressure differential between a point in the supply system at which the static pressure head is substantially less than the total head and a point in said headbox below'the level of stock therein and at a zone of quiescence, and

indicating means associated with said pressure measuring means for indicating the measured pressure differential.

4. A papermaking machine comprising,

a stock headbox for receiving stock from a pressurized supply system and having a slice opening for directing a flow of stock to a paper forming apparatus,

means for determining the difference in static pressure of the stock in said headbox at a quiescence zone and in a point in the supply system at which the static pressure head is substantially less than the total head, and

indicating means associated with said pressure differential determining means for indicating said pressure differential and for indicating the discharge velocity head of stock flowing from said slice opening as a function of said pressure differential.

5. In a papermaking machine having: a headbox for receiving pressurized stock from a stock supply system and having a slice opening for directing a flow of stock from said headbox to paper forming apparatus, the improvement of means for measuring the discharge velocity head of the stock flowing from the slice opening comprising,

a manometer having three upwardly extending leg members interconnected at the bottom ends thereof,

a quantity of fluid of a known specific gravity in said manometer for pressure-indicating displacement purposes,

first conduit means communicating the top of one of said legs to a point in the headbox below the level of stock therein and at a zone of quiescence, and

second conduit means communicating the top of another of said legs to a point in said stock supply system where the static pressure head is substantially less than the total head whereby the difference in elevation of said fluid in said legs is a function of the difference in static pressure between said zone of quiescence and said point in said stock supply system which, in turn, is a function of the discharge velocity head of stock flowing from said slice opening.

6. A papermaking machine comprising,

a stock supply conduit for supplying pressurized stock from a source,

a stock headbox for receiving stock. from said supply conduit and having a slice opening for directing a flow of stock to paper forming apparatus,

first and second standpipe members connected, respectively, to said headbox and to the wall of said supply conduit and in open communication respectively with said headbox below the level of stock therein and at a zone of quiescence and with the interior of said supply conduit at a point at which the static pressure head is substantially less than the total head,

a tap connection on each of said standpipes, and manometer means connected to each tap connection for measuring the difference in static pressure between the zone of quiescence and the point of said supply 1 1 conduit which, in turn, is a function of the discharge velocity head of stock flowing from the slice opening.

7. A papermaking machine as defined in claim 6 wherein the tap connection in said first standpipe is located at the same vertical elevation as the slice opening.

8. A papermaking machine as defined in claim 7 wherein the tap connection of the second standpipe is at the same vertical elevation as is the tap connection of the first standpipe.

9. A papermaking machine comprising,

a stock supply conduit for supplying pressurized stock from a source,

a stock headbox for receiving stock from said supply conduit,

said headbox being closed at the top thereof for purposes of pressurization and having a slice opening for directing a flow of stock to paper forming apparatus, first and second closed standpipe members extending in a vertical direction and connected respectively to said headbox and to the wall of said supply conduit, said standpipe being in open communication at the tops thereof with the top of said headbox to said leg members to the top connection of said first standpipe, and second conduit means communicating the top of the other of said leg members to the top connection of said second standpipe.

References Cited UNITED STATES PATENTS 2,901,040 8/1959 Gade 162-340 X 3,074,476 1/1963 Gorbin et al. 162-34O X S. LEON BASHORE, Primary Examiner. 

1. A PAPERMAKING MACHINE COMPRISING, A STOCK HEADBOX FOR RECEIVING STOCK FROM A SUPPLY SYSTEM, A SLICE OPENING FOR DELIVERYING STOCK TO A PAPER FORMING APPARATUS SUCH AS A FORMING WIRE, A CHANNEL FOR CONVENING THE STOCK FROM SAID HEADBOX TO SAID SLICE OPENING AND PRODUCING A REDUCTION IN THE STATIC PRESSURE OF THE STOCK THERETHROUGH DUE TO FRICTION LOSSES, PRESSURE MEASURING MEANS FOR CONNECTION TO THE SUPPLY SYSTEM AND TO SAID HEADBOX FOR DETERMINING THE PRESSURE DIFFERENTIAL BETWEEN A POINT IN THE SUPPLY SYSTEM AT WHICH THE STATIC PRESSURE HEAD IS SUBSTANTIALLY LESS THAN THE TOTAL HEAD AND A POINT IN SAID HEADBOX BELOW THE LEVEL OF STOCK THEREIN AND AT A ZONE OF QUIESCENECE. 